1. Field of the Invention
The present invention relates to a method for fabricating a liquid crystal display (LCD) device. More particularly, the present invention relates to an apparatus and method for rubbing an alignment layer of an LCD device, in which rubbing uniformity of the alignment layer is improved.
2. Discussion of the Related Art
Generally, LCD devices are widely used for clocks, calculators, monitors for PCs, notebook computers, TVs, monitors for spacecraft, PDAs, cellular phones, etc. LCD devices are used because of their characteristics and they have the advantages of low voltage driving, low power consumption, full color, thin profile, and lightness in weight.
LCD devices may be classified into LCD panels for displaying images and circuits for driving the LCD panels.
An LCD panel may include a thin film transistor (TFT) substrate provided with a TFT array, a color filter (CF) substrate provided with a color filter array, and a liquid crystal layer formed between the two substrates. Alignment layers may be respectively provided on each surface of the TFT substrate and the CF substrate to face each other. The alignment layers determine an alignment direction of the liquid crystal layer.
The TFT substrate may include a plurality of gate lines arranged along a first direction at fixed intervals and a plurality of data lines arranged along a second direction perpendicular to the first direction at fixed intervals to define pixel regions. The TFT substrate may also include a plurality of pixel electrodes formed in each of the pixel regions to display images and a plurality of thin film transistors that may be switched on/off by driving signals of the gate lines to transfer image signals of the data lines to the respective pixel electrodes.
The CF substrate may include a black matrix layer that prevents light from reaching the pixel regions, R/G/B color filter layers corresponding to the respective pixel regions to display various colors, and a common electrode formed on the entire surface including the color filter layers. The common electrode may be formed on the TFT substrate in an in-plan switching (IPS) mode LCD device. An alignment process may then be performed for the alignment layers of the TFT substrate and the CF substrate to arrange liquid crystal molecules.
An example of the alignment process includes a rubbing method in which a surface of an alignment layer is rubbed with a rubbing cloth. The rubbing cloth is adhered to an outer circumference of a roller. If the roller is rotated, the rubbing cloth adhered to the outer circumference of the roller contacts the surface of the alignment layer so that the surface of the alignment layer is rubbed with the rubbing cloth.
If liquid crystal molecules are arranged along a direction of the alignment layer rubbed with the rubbing cloth, it may be possible to obtain uniform display characteristics.
FIG. 1 is an elevational view illustrating a portion of a related art LCD device.
As shown in FIG. 1, an upper substrate 10 and a lower substrate 30 are spaced apart from each other at a certain interval and face each other. A liquid crystal layer 50 is interposed between the upper and lower substrates 10 and 30.
The lower substrate 30 includes a plurality of gate lines 32, a plurality of data lines 34, and a plurality of TFTs T. The gate lines 32 cross the data lines 34. The TFTs are formed at regions where the gate lines 32 cross the data lines 34.
Also, pixel regions P are defined by the regions where the gate lines 32 cross the data lines 34. The pixel regions P are provided with pixel electrodes 46 connected with the TFTs T.
Furthermore, each of the TFTs T includes a gate electrode (not shown) and source and drain electrodes (not shown). A gate voltage may be applied to the gate electrode and a data voltage may be applied to the source and drain electrodes. Each of the TFTs T also includes a channel (not shown) for controlling the voltages to be on/off using the voltage difference between the gate voltage and the data voltage.
The upper substrate 10 includes a color filter layer 12 and a common electrode 16. The color filter layer 12 includes a color filter (not shown) and a black matrix (not shown). The color filter only transmits light corresponding to a specific wavelength. The black matrix is arranged at the boundary of the color filter and shields light from the pixel regions P of the lower substrate 30, where alignment of the liquid crystal molecules is not controlled.
An upper polarizing plate 52 and a lower polarizing plate 54 are respectively arranged outside the upper and lower substrates 10 and 30 and transmit light only parallel to a polarizing axis. A separate light source, i.e., a back light, is arranged below the lower polarizing plate 54.
A related art method for rubbing an alignment layer of an LCD device will be described with reference to the accompanying drawings.
FIGS. 2A to 2C illustrate a related art process for rubbing an alignment layer. FIG. 2A is a perspective view illustrating an apparatus for rubbing an alignment layer, FIG. 2B is a side view illustrating an apparatus for rubbing an alignment layer, and FIG. 2C is a plan view illustrating an apparatus for rubbing an alignment layer.
As shown in FIGS. 2A to 2C, the related art apparatus for rubbing an alignment layer includes a cylindrical rubbing roller 61, a rubbing cloth 62 adhered to an outer circumference of the rubbing roller 61 using a double-sided tape, a rotary shaft 63 connected with both sides of the rubbing roller 61 and rotated along one direction while supporting the rubbing roller 61, and a rotary motor 66 connected with the rotary shaft 63 to rotate the rotary shaft 63.
A related art method for rubbing an alignment layer using the aforementioned rubbing apparatus will now be described.
A substrate 64 provided with an alignment layer 65 is loaded on a stage 60, and a driving roller is rotated by a driving motor (not shown) so that the stage 60 advances along an arrow. The driving motor is to move the stage 60 in one direction.
The rubbing roller 61 connected with the rotary shaft 63 contacts the alignment layer 65 of the substrate 64 loaded on the stage 60 at the bottom, and forms a groove on a surface of the alignment layer 65 while being rotated by the rotary motor 66 in one direction.
That is, the related art rubbing process is performed in such a manner that the rubbing roller 61 wound with the rubbing cloth 62 is rotated to rub the surface of the alignment layer 65 using physical friction.
In order to obtain uniform display characteristics in the LCD device, it is important that the groove is uniformly formed in a wide area. The groove can uniformly be formed by rubbing the surface of the alignment layer with the rubbing cloth at uniform pressure and speed to align a high molecular chain on the surface of the alignment layer in a certain direction.
The aforementioned related art method for rubbing an alignment layer uniformly arranges the liquid crystal molecules by rubbing the alignment layer with the rubbing cloth. The related art method also uniformly displays images on the entire surface of the LCD device by arranging the alignment layer in one direction.
However, with the trend towards larger sized LCD devices, LCD devices having dimensions of 1100 mm or greater have been commercially used. Under these circumstances, the rubbing roller used for the rubbing process is contrived to have a large size.
In this case, as shown in FIG. 3, a middle portion in a longitudinal direction of the rubbing roller 61 is bent by self-load as the rubbing roller 61 of metal material has a longer cylindrical length. Also, the alignment layer 65 formed on the substrate 64 is rubbed by uneven pressure. As a result, display quality is deteriorated over the entire surface of the LCD device.
Furthermore, for the alignment process, the rubbing roller 61 is adhered with the rubbing cloth 62 using a general adhesive. Furthermore, static electricity occurs due to friction between the rubbing cloth 62 and the alignment layer 65. Friction is caused by rotation of the rubbing roller 61. For this reason, dust, dirt in the air, and/or particles generated from the rubbing cloth 62 is adsorbed into the alignment layer 65, thereby causing a pin hole.